Pugmill



Sept. 29, 1942. R. G..BELLEZZA arm. 2,297,646

PUG MILL Filed March 9, 1940 RUSSELL q. BEL| EzzI= ED RRD M. SKIPPER Patented Sept. 29, 1942 NT GHQ PUGMILL land Application March 9, 1940, Serial No. 323,241

2 Claims.

The invention relates to a method of handling porcelain clay and more particularly to a method of and/ or apparatus for preventing the creation in the pugging of ceramic clay of stresses and strains in the pug.

The principal object of the invention, generally considered, is to provide as a part of the pug mill nozzle, or as an attachment thereto, mechanism for preventing the ceramic material from rotating with respect to the pug mill nozzle during its longitudinal passage therethrough.

Other objects and novel features of the invention will be hereinafter pointed out in connection with the detailed description of a preferred embodiment of the invention illustrated in the accompanying drawing, in which:

Figure 1 is a fragmentary vertical cross-sectional view through the pug mill and nozzle, illustrating one form of our invention.

Figure 2 is a cross-section taken on the line 22 of Figure 1.

Figure 3 is a cross-section taken on the line 33 of Figure 1, looking in the direction indicated by the arrows adjacent the ends of the said line.

Figure 4 is a cross-section on the line 44 of Figure 3.

Figure 5 is an elevational view of a modified form of spider.

Figure 6 is a cross-section taken on the line 66 of Figure 5.

It has long been customary in the production ofceramic material to eliminate mauling and manual working of the clay by taking the clay disks from the filter press and causing the same to be thoroughly mixed and commingled by means of a pug mill, such mills comprising generally a cylindrical tank portion provided with a rotatable screw of the endless type, causing the bats of clay, or portions of the filter cake, to be forced together and thoroughly commingled. At the bottom of the pug mill there is provided a trough portion in which is rotated another endless screw, the screw terminating outside of the body of the pug mill and preferably in the nozzle portion, or immediately in rear of the nozzle portion through which, by means of this horizontal screw, the thoroughly commingled ceramic clays are forced from the nozzle as a solid or hollow tube as desired and are cut into desired lengths by the operator positioned at the extremity of the nozzle.

It has been known for a number of years that no matter how uniform the clay may be that is placed in the pug mill, so far as the composition and moisture content are concerned, such clay, when forced from the pug mill nozzle has a tendency to separate into a plurality of strip-s corresponding to the blades on the extrusion screw. It has also been known that, if a pug of any given length were placed in an upright position and had inscribed on the surface a straight line substantially parallel to the axis of the pug, upon drying of this pug marked as indicated, the line would tend to follow and in a great many instances would follow the degree of curvature of the extrusion screw, showing that the pug, despite its amorphous composition, possessed certain strains and stresses for which no one had been able to account.

In the plant in which this invention was developed both solid and hollow pugs were produced in large numbers practically every day. Careful examination of the pugs disclosed the fact that the thinner the walls of the pug the less was the loss in the drying and firing of such insulators. Where the insulators were formed from r a solid pug the drying andfiring loss reached alarming proportions. It was determined, therefore, to run a series of experiments and attempt, by these experiments, to ascertain the cause of these drying and firing losses and also to determine whether it was possible, either in the treatment of the clay or in the modification of the pug mill, to overcome-the latent defects of the material and in such manner eliminate or reduce to a minimum the drying and firing losses on this class of material.

In carrying out the experiments one of the pug mills was equipped with a member connected to the end of the shaft on which the extrusion screw rotated. This member projected into the nozzle and was of cruciform shape so that upon the extrusion of pug there was formed in the center of such pug a recess of cruciform shape. It was found upon drying that the center of the pug rotated approximately three degrees for every foot of length. It was also found that the greatest rotative tendency existed at the center of the pug and decreased rapidly toward the periphery. It was also found that upon firing of the dry pugs the tendency to rotate, which the drying of the pug diminished, immediately returned when the pug was sufliciently softened by heat to permit these forces to act and that it was the rotative forces which created not only the cracks after drying but which also resulted in the destruction of the finished product during the firing stage.

Having determined, as the result of these experiments, that it was the rotative tendency or the actual rotation of the center of the pug with respect to its periphery which caused the large drying and firing losses, the problem of preventing such rotation was next undertaken and it was found that by providing a ball-shaped member at the end of the extrusion screw, which caused the clay on its passage to be forced outwardly toward the periphery and then to fiow inwardly toward the center, such action eliminated the rotative tendency at the center and permitted formation of a pug in which no rotation of the center of the pug with respect to its periphery could be discovered either in the drying or firing. It was found, however, that since the end of the extrusion screw was free, the strains caused by the clay flowing past the ball tended to prevent the free movement of the screw shaft and consequently set up in the apparatus objectionable vibrations. It was, therefore, decided to interpose between the end of the pug mill nozzle and the base of the extrusion nozzle a spider to support the ball, and thus free the extrusion screw from the support of the ball. It was further discovered that if the legs of the spider were streamlined, that is were made elliptical in cross section with the greater axis of the ellipse extending lengthwise of the extrusion nozzle the side portions of the legs acting upon the clay produced sufiicient drag to prevent the rotation of the central portion of the clay and rendered the ball unnecessary.

As shown on the drawing and initially considering the species of Figures 1 to 4, there is provided between the pug mill nozzle l and the base 2 of the extrusion nozzle 3 a spider 4, said spider being preferably provided with three legs 5 each spaced one hundred and twenty degrees (120) from the other. Each leg is semi-elliptical in cross section, having the greater axis 6 thereof arranged substantially parallel to the longitudinal axis of the extrusion nozzle. The spider may be provided with a solid center 1 having therein a threaded recess by which there is connected and positioned within the extrusion nozzle a plunger 8 of any desired configuration to produce a hollow pug. The plunger 8 is preferably provided with a universal joint 9 adjacent the threaded end so that it may assume any position and will tend to occupy a central position in the pug as the same is projected through the exit end In of the extrusion nozzle.

In the embodiment of the invention illustrated in Figure 1 we have shown the universal joint between the parts 8 of the plunger formed as an elliptic-shaped ball I l, the latter serving to cause the clay projected from the pug mill nozzle by the screw I2 to fiow outwardly and hence to be forced so intimately into contact with the main body of the pug adjacent the point 13 at which the nozzle 3 narrows that all tendency of the central portion of the pug to rotate with respect to its periphery is prevented.

In place of the combined spider and ball II we find it convenient to use a slightly modified form of spider, as shown in Figures 5 and 6, the modification consisting in forming the legs 5' of the spider 4 as complete ellipses with their greater axes 6' arranged parallel to the longitudinal axis of the extrusion nozzle 3, the increased longitudinal surface area of the legs 5' serving to overcome the rotative tendency of the central portion of the pug with respect to its periphery and thereby prevent this rotation. It will be obvious that either form of spider can be utilized by disconnecting the bolts I i which extend through the base 2 of the extrusion nozzle 3 and through the flange l5 of the pug mill nozzle I and of course through suitable apertures in the rim l6 of either spider. We have illustrated the end I! of the plunger 8 which is positioned adjacent the open end ID of the extrusion nozzle, of cruci-form shape although it Will be understood that this is merely for the purpose of illustration and that other conformations may be used as desired.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

l. The combination with a pug mill for use in the mixing of porcelain clay, of an extrusion nozzle circular in cross section, the cross sectional area of said nozzle being gradually diminished from the point of connection with the mill to its orifice, an extrusion screw Within said mill, said screw terminating short of said connection between said mill and nozzle, a spider positioned adjacent the base of said extrusion nozzle and rigidly connected to said mill and nozzle, means on said spider comprising a plurality of arms extending radially from the center of said spider for preventing the rotation of the extruded clay pug during the passage through said nozzle, a rigid member connected at one end to said spider, said member having intermediate its ends a ball and socket joint connection, the opposite end of said member extending to the nozzle orifice, said member being adapted to be positioned centrally of said orifice by the passage of the clay pug and being adapted to form therein a central longitudinal opening, said opposite end of said member being of lesser cross sectional area than said ball and socket joint connection.

2. The combination with a pug mill for use in mixing porcelain clay, of a nozzle member circu lar in cross section, said nozzle member being connected to said mill, the cross sectional area of said nozzle gradually decreasing from its point of connection to its orifice, a spider member interposed between said mill and nozzle and rigidly connected to both of said members, said spider comprising a central hub and a plurality of radia arms intersecting the orifice of said pug mill, and a member rigidly connected at one end to said hub, said member comprising a pair of members connected by a ball and socket joint, the socket member having a portion of its exterior surface substantially concentric with the adjacent surface of said nozzle, the opposite end of said member being of lesser cross sectional area than said ball and socket joint and terminating substantially in the plane of said orifice, said member being adapted to be positioned centrally of said orifice by the passage thereabout of the extruded clay pug.

RUSSELL G. BELLEZZA. EDWARD M. SKIPPER 

